It's not a good idea to automatically retry internally at the lruttl
layer, as there is no bound on the retries and not enough context in the
cache layer to decide if we really should retry.
This commit removes the `retry_on_sema_timeout` flag from lruttl
and replaces the implementation of the mod-memoize
retry_on_populate_timeout flag with a simple 3 attempt retry
loop in the failure case.
Importantly, those retries in mod-memoize have the opportunity
to adjust to a bumped ConfigEpoch, which is important for the
pathological situation where a flood of changes stream in from
TSA daemon and there is a delay in handling populate, and the
cache capacity is not sufficient to accommodate that run
of epoch bumps.
Wez Furlong
d5e3d6a82a